1. Field of the Invention
This invention relates to a nickel-base alloy welding material for use in welding of steels which are intended to be subjected to super low temperature.
2. Description of Prior Art
Nine percent nickel steels are frequently used as lining materials for vessels for transporting super low temperature liquids, such as liquefied nitrogen, liquefied oxygen and liquefied natural gas. They are also used in the construction of equipment used for processing or storing super low temperature liquids. According to ASTM standards, 9% nickel steels are classified into A 353-65T (NNT steel) and A 553-65T (QT steel), and their properties are standardized. According to this standard, each of these types must have a tensile strength of 70.3 - 84.4 Kg/mm.sup.2, and the yield point (0.2% proof stress) for the NNT steel must be above 52.7 Kg/mm.sup.2, and for the QT steel must be above 59.8 Kg/mm.sup.2. The low temperature toughness at -196.degree.C. must exceed 3.5 Kg-m.
Nickel steels of 5.5% have also become commercially available, but so far there has been no standardization of such material. The strength and low temperature toughness of such materials, however, are almost equal to those of 9% nickel steels.
It has been considered to use so-called eutectoid materials for 9% nickel steel and nickel-base alloys as the welding materials for the above mentioned low temperature steels.
The eutectoid welding materials are of the same composition as that of the base metal and are characterized by a tensile strength and a yield point equal to those of 9% nickel steels. However, since the low temperature toughness at -196.degree.C. in the as-welded state, of these eutectoid materials, is inferior to that of the base metal, they have not been widely used.
Although nickel-base alloy welding materials are insufficient from the point of view of tensile strength (60-65 Kg/mm.sup.2) and yield point (0.2% proof strength) and 36 - 40 Kg/mm.sup.2, respectively, for the deposited metal, each of which is lower than the corresponding property of the base metal, its low temperature toughness in the as-welded state is stable and excellent, and it has been primarily used for low temperature applications.
Welding materials of this type are classified as AWS A5.11 ENi-Cr-Fe 1 to 3 and include so-called inconel alloys of 75Ni-15Cr series and alloys of 50Ni-15Cr and 35Ni-15Cr series, etc.
Since in such welding material a higher nickel content results in a high strength and a more stable impact resistance, the inconel alloys frequently find the greatest range of use.
ASTM standard 1308-5 specifies the properties required of the weld zone so far as when stress relief annealing is not conducted in the manufacture of pressure vessels by welding of super low temperature steels, and this standard is usually adopted in this field. This standard provides the requirements of joint tensile strength. Even though inconel alloys provide lower strengths of the whole deposited metal than 9% nickel steels, they can nevertheless fully meet the requirements specified by ASTM 1308-5. In other words, any material that can provide a whole deposited metal strength of about 60 to 65 Kg/mm.sup.2 can meet the standards of ASTM 1308-5, which means that this standard has been determined by recognition of the fact that the strength of the weld zone may be lower than that of the base metal. In designing pressure vessels according to this standard, the lower strength weld zone must be considered, which results in a greater thickness of construction than would be required if the weld zone were of equal strength.
The Witherell reference U.S. Pat. No. 3,026,137 discloses the use of a nickel chromium alloy which contains, in percent by weight, from about 10% to about 30% chromium, up to about 8% iron, from about 2% to about 3.5% titanium, up to 7% manganese, up to about 2% columbium, up to about 0.5% silicon, up to about 0.1% carbon, and the balance essentially nickel, with the nickel content being at least about 65%.